WWW Error : 404 with working url

Hi there. Can't get out of my 404 error !

My php request works fine in editor, but when I build ( Webgl ), it returns me a 404 Not Found ( the url is still correct in the log )

my code can't be easier, I call this coroutine :

 public  IEnumerator WaitRequest( WWW request, Risque[] risques)
 {
     yield return request;

     // check for errors
     if (request.error == null)
     {
         Debug.Log(request.url + "WWW Ok!: " + request.text);
     }
     else {
         Debug.Log(request + " url " +request.url+  "  WWW Error: " + request.error);
     }
     yield return null;

 }

Editor return the response, the build return " WWW Error: 404 Not Found " both in Chrome and Mozzila.

Any ideas ? Thanks in advance !

Ok little update : Found in my console that my request was modified ( and i don't not why ) to something like : htp://Adresse/ShouldNot/Be/Added/ MyGoodUrl

So my url is good in the log but when the request is launched the address of the current page is added before my url .... And the 404 is logical....

Why is my request modified ?